Micro-optical devices are optical devices having microstructure whose size is above submicron level and surface roughness up to nanometer level. Generally, micro-optical devices on-chip significantly increase the interaction of light and matter by spatially and even temporally localizing the optical field. These devices have important applications and development prospects in fundamental research and engineering applications, such as quantum optics, nonlinear optics, quantum electrodynamics, photonics, low threshold maser, ultra-small filter, biosensor, optical gyroscope, optical frequency comb and so on. In the application, microdisc cavity and microring cavity limit light to a small volume for a long time through consecutive multiple total internal reflection at the circular boundary between the medium cavity and the surrounding environment. They have a rather high-quality factor and a very small mode volume, which can greatly enhance the interaction between light and matter.
Optical waveguide on-chip is the basic component of the micro-optical devices on-chip. The high refractive index difference between the waveguide material and the environment is used to bind the light in the optical waveguide, generally showing strong interaction between light and material and low transmission loss.
An integrated device is composed of the micro-cavity and micro-cavity, micro-cavity and optical waveguide, and optical waveguide and optical waveguide, and has controllable coupling efficiency and extremely low insertion loss, and its preparation is difficult in micro optical integration on-chip. Currently, mainstream micro optical devices on-chip, such as microdisc cavity (See Lin, Jintian, et al., “Fabrication of high-Q lithium niobate microresonators using femtosecond laser micromachining,” Scientific Reports 5 (2015): 8072; Wang, Jie, et al., “High-Q lithium niobate microdisk resonators on a chip for efficient electro-optic modulation,” Optics Express 23.18 (2015): 23072-23078), microring cavity (See Zhang, Mian, et al., “Monolithic ultra-high-Q lithium niobate microring resonator,” Optica 4.12 (2017): 1536-1537), and optical waveguide (See Zhang, Mian, et al., “Monolithic ultra-high-Q lithium niobate microring resonator,” Optica 4.12 (2017): 1536-1537), are manufactured by semiconductor photolithography or femtosecond laser combined with focused ion beam (FIB) etching. The two technologies have been relatively mature in preparation of microstructure on material surface. However, the former is only suitable for processing semiconductor film material or silicon dioxide film, and often faces difficulties when faced with a medium film that is difficult to be chemically treated, such as lithium niobate, and it is also difficult to prepare high quality structures in millimeter or even centimeter level. The latter is limited by processing efficiency of FIB and faces problems in preparing large-size structures and large-scale integration.
Traditional chemical mechanical polishing is used to prepare a flat material surface, not for the preparation of micro-optical structures on-chip.